In certain high speed rotating equipment with static excitation, such as large turbine-generator systems, carbon brush current collection systems are utilized in conducting a field current to the generator rotor. The collector sets typically comprise a pair of collector rings, or one for each pole, mounted on the rotor and a set of stationary brushes angularly displaced around, and in contact with, each collector ring. In order to protect the collector sets and to prevent inadvertent contact with them by personnel, they are usually housed within an enclosure which includes a fixed base. This enclosure is commonly referred to as a collector house. Typically the collector house includes stationary traverse end walls having sealed openings through which the rotor shaft passes and a house defining the roof and sidewalls of the enclosure.
Because of high energy demands, it is common to arrange several carbon brushes within a magazine or gang type brush holder. Several brushes, normally six, are grouped within the brush holder, a plurality of which are arranged around the outside diameter of the generator rotor. Examples of such brush holders are described in U.S. Pat. No. 3,387,155, issued on Jun. 4, 1968, and U.S. Pat. No. 3,710,478 which issued on Jan. 16, 1973.
In synchronous generator excitation systems the field windings require a continuous source of power, and the excitation system must be sized to draw the maximum energy and power from either the local system for a static excitation system, or from the shaft for a brushless system. FIG. 1 illustrates an example of a static excitation system. The generator rotor 2, disposed in the AC windings 4, has a protruding shaft 6. The static excitation system 8, which comprises an excitation transformer followed by a large power rectifier and associated controls, draws power from the local grid 10 which provides power to the shaft 6, though carbon brushes 12 and slip rings 14.
These types of excitations systems, however, are complicated and expensive, since they draw power from the grid and require the installment of electrical components. In the prior art, even if the excitation system drew power directly from the generator, since the generator is still part of the local grid, the input voltage to the excitation transformer would still drop too low to use.
What is needed is an excitation system that does not rely on an external power supply, and is simple to install and use. Other difficulties with the prior art also exist, some of which will be apparent upon further reading.